Abstract Air pollution is a major public health concern in the US and worldwide. Exposure to air particulate matter (PM) with an aerodynamic diameter <2.5 [unreadable]m (PM2.5) is well known to increase cardiovascular incidence and mortality. Inhaled PM2.5 induces systemic pro-inflammatory response and oxidative-stress, two major cardiovascular disease (CVD) pathways. Blood leukocyte gene expression profiling in highly PM-exposed subjects has revealed that systemic inflammatory responses are initiated through extensive gene expression shifts but mechanisms regulating the gene expression changes are largely unexplored. MicroRNAs (miRNAs) are small RNA molecules that have newly emerged as key regulators of gene expression. Inflammation and oxidative stress have been shown to alter miRNA expression, which can be controlled by their encoding gene DNA methylation status. Our preliminary data have shown that PM2.5 exposure changed the expression levels of certain miRNAs in blood leukocytes in a highly PM-exposed population. We hypothesize that PM exposure- induced oxidative stress and inflammatory response may cause blood leukocyte miRNA expression changes that regulate gene expression profiles. Gene expression alterations may then cause certain changes in circulating biomarkers and cardiovascular physiology to favor CVD development. We propose to test these hypotheses using data from the Beijing Truck Driver Air Pollution Study (BTDAS), our recently completed study in Beijing, China, one of the most polluted cities in the world. Thanks to special funding by the Italian Ministry of Scientific Research, the BTDAS was conducted shortly before the Beijing 2008 Olympic Games (June 15 to July 27, 2008). Two groups of subjects were recruited, i.e., 60 truck drivers (high exposure) and 60 indoor workers (low exposure). We collected personal PM2.5 and its toxic metal exposure data via air monitors and continuous EKG data via Holter monitors during their work hours, and blood samples at the end of work, on two independent work days with 1-2 week intervals. We propose to conduct an ancillary study to 1) identify PM2.5- and its toxic metal-related miRNA expression signatures by performing an unbiased screening of miRNAs using highly quantitative Next Generation Sequencing;2) examine whether miRNA expression is associated with encoding gene methylation status;3) determine whether PM-related miRNA signatures are associated with CVD measures using our already measured data on plasma inflammatory and blood clotting markers, blood pressure and EKG. Given the general public's ubiquitous exposure to air pollution, this research is of high significance. This study is designed to take full advantage of the unique specimen repository as well as previously collected data and examined measures to potentially identify novel mechanisms linking air pollution with CVD, and thus provide the potential to identify important CVD preventive strategies.